The Japanese Beetle Is Invasive Pest Threatening Oregon (Part 2)

Serving Families Throughout Portland & the Pacific Northwest

If you have not already read it, here’s a link to Part 1 of this post.


Because they are flyers, the beetles spread naturally and often fly short distances between plants.  In fact, they have the capability to fly up to 5 miles with the help of the wind-seems crazy, right?

This explains how they gradually reach adjacent areas but traveling long distances or being introduced to a new area requires human help, albeit involuntary and usually related to commerce.

How does this happen?  Well, the larva (or grubs) live in soil so any plants or soil imported from infested areas could easily contain them whereas adult beetles can hitch a ride on all types of vehicle or cargo.

Quarantines help stop the spread

For these reasons, Oregon put a quarantine in place to regulate the importing of plants from infested states.  Part of this enforcement includes the ODA routinely inspecting cargo planes that arrive from infested areas during the adult flight season (late June to end of August).

Even with strict policies in place, they still manage to periodically pop up in our state, which is why ODA places thousands of Japanese Beetle traps around the state.  They can then track them and if necessary, put a plan into place for getting rid of this pest.


  • Egg
  • Larva (or grub)
  • Pupa
  • Adult

In her lifetime, one female beetle lays 40 to 60 eggs buried 5 to 7.6 cm deep in the soil. The eggs take 2 weeks to develop and hatch during July and August.  The grubs feed on the roots of turf grass and vegetable seedlings and are mostly full grown by September.

To survive the cold winter months, they burrow deeper into the soil and stay there until spring, when they move up to the root zone to feed for 4 to 6 weeks.

Fully grown grubs pupate in an earthen cell where they remain pupae for around 2-3 weeks and later, emerge as adults anywhere from late June to early August.

The adult beetle is a bright metallic green with copper-brown wing covers and 7/16” long.  It has 2 distinctive tufts of white hair right behind its wing covers and 5 patches of white hair long its sides.

Mating takes place right away since adults only live around 30 to 45 days.  After mating, the females lay their eggs in the soil and the whole cycle begins again.

Why is the Japanese beetle harmful to Portland?

We consider them to be so harmful to the Portland area because we have so many trees, flowers, berries and plants upon which they love to feed.

  • Adults love to feed on rose blossoms and foliage from many other ornamental garden plants.
  • Beer and wine are 2 of our biggest exports & favorite beverages and adults love to feed on the foliage of hops and wine grapes.
  • Grubs live underground and feed on the roots of grass and plants so lawns, golf courses, parks and all grassy areas are in danger.
  • Plants, fruits, vegetables, etc. from states that have the Japanese Beetle cannot be sold to states that don’t have the pest without going through rigorous and expensive inspections.
  • The beetles are drawn to one another and dine in groups eating plants down to the stems.
  • If not eradicated, they will be here to stay and you’ll have yet another pest to fight.

While homeowners might think of them as a nuisance, farmers and business owners have the potential to lose a lot of money if they make Oregon their new home.


You may think that there’s nothing you can do to help but that’s not the case.  Here are some easy things you can do to help us track the beetles and aid in our fight again this invasive species.

  • If you spot any Japanese beetles on your property, please contact the ODA.
  • Any beetle damage to your lawn, roses, grapes, fruits or other trees/shrubs needs to be reported to the ODA.
  • Allow ODA survey staff to place traps on your property during the summer.
  • Follow quarantine regulations that ban the movement of plants and soil from infested eastern states UNLESS it’s certified by state agricultural officials to be free of the Japanese beetle or has been treated to eliminate any beetle life stages.

Gardening practices for living with Japanese beetles

If you live in Cedar Mills where the beetles have been spotted, here’s a list of practices you should put in place to help fight them.

  • Leave grass clippings on your lawn
  • Larvae need lots of moisture so don’t water your lawn June 1-Oct. 30
  • Don’t aerate or use power rakes on your lawn
  • Keep plants healthy by following the recommended schedule for fertilizing and watering
  • Plant things that adult beetles avoid, like lilac, dogwood or ornamental evergreens.
  • Encourage natural enemies with flowering plants that produce nectar and pollen.

To learn more about how the ODA is dealing with this pest, you can read our blog post entitled General Tree Service Chosen by ODA for Japanese Beetle Eradication Program. 

The post The Japanese Beetle Is Invasive Pest Threatening Oregon (Part 2) appeared first on General Tree Service.

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